Revitalizing small offshore oil assets — Field redevelopment feasibility study

Abstract

During the last two decades, several small size offshore fields in the North Sea have been developed and exploited by tie-in development strategies to existing infrastructure supplied by the nearby large hydrocarbon fields and/or pipeline transportation systems. The field under consideration is such an example. However, achieved oil recoveries lower than expected (~ 18%) led to the abandonment of the asset and removal of the field's supporting fluid transportation lines and cables approximately two years from the onset of oil production. Since then, a change of field ownership and several subsurface studies sparked a new interest of a possible field redevelopment. This work investigates and evaluates the potential standalone field redevelopment of a small North Sea oil field through the deployment of a gas injection process that utilizes the produced gas as the key enhanced oil recovery (EOR) agent. A field-sector, compositional simulation model is constructed to evaluate and compare the most promising gas-based EOR techniques such as continuous gas injection, water alternating gas and simultaneous water and gas injection processes against water injection. Several sensitivity studies are conducted to optimize the conditions/parameters of the selected EOR technique and practical issues that can influence oil recovery factors are evaluated for a potential pilot or field-wide scale implementation. The results indicate that the implementation of a Simultaneous Water and Gas (SWAG) EOR injection process that makes use of the field produced gas and having undergone a thorough and field-wide optimization of operational parameters (produced gas availability, fluids injection rate, injection water–gas ratio, production and injection well BHP, fluids injection scheme, etc.) as well as a careful investigation of potential well interventions to increase oil production (selective re-perforation of existing wells, possible shutoff of excess water, etc.) could be a viable EOR technique for redeveloping this asset.